Impurities in SiO2 films deposited by plasma-enhanced chemical vapor deposition using tetraethoxysilane

SiO₂ films were prepared by plasma-enhanced chemical vapor deposition (PECVD) using tetraethoxysilane (TEOS) and N₂O. The Si(SINGLE BOND)OH concentrations in the films deposited at a low temperature (200 °C) were found to be below the detection limit of Fourier-transform infrared spectroscopy (FTIR) with an RF power of more than 80 W. Optical emission spectroscopic study for SiO₂ deposition in the gas phase showed that emission intensities of both atomic oxygen and atomic hydrogen depended strongly on RF power. Further mass spectrometric study in N₂O plasma indicated that atomic oxygen increased with RF power due to decomposition of N₂O to N₂ and O. In addition, we tried to prepare SiO₂ films using TEOS and He in order to study the role of oxidants. It was found that low-impurity SiO₂ films can be obtained at temperatures lower than 200 °C with higher RF power through the effects of oxidation by atomic oxygen and electron impact decomposition. © 1998 Scripta Technica. Electr Eng Jpn, 121(4): 11–17, 1997     

Polyether-segmented nylon hemodialysis membranes. III. Preparation and properties of new polyether-segmented nylon

In order to apply a blood-compatible polymer to hemodialysis membrane, a new polyether-segmented nylon which dissolved in common organic solvents was designed. The basic polyether-segmented nylon was synthesized by melt polycondensation from sebacic acid, m-xylenediamine, and α,ω-bisaminopropyl-poly(ethylene oxide). To improve the solubility, azelaic acid and hexamethylenediamine were copolycondensed with the basic copolymer. The solubility was correlated with the heat of fusion (ΔH_m) of the copolymer. When ΔH_m is < 30 mJ/mg, the polymer is soluble in dimethylsulfoxide and makes a stable solution. The nonthrombogenicity was investigated in the viewpoint of adhesion of platelet onto the copolymer surface. It is made clear that the surface of the block copolymer, having > 10 wt % of poly(ethylene oxide), suppresses the adhesion of platelet, and the composition of the nylon block has no effect on the adhesion of platelet. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:1723–1729, 1997     

Application of porous microspheres prepared by SPG (Shirasu porous glass) emulsification as immobilizing carriers of glucoamylase (GluA)

Fairly uniform spheres of crosslinked polystyrene (PS) and polymethyl methacrylate (PMMA), prepared by a particular emulsification process using SPG (Shirasu Porous Glass) membranes and subsequent suspension polymerization, were applied for immobilizing carriers of Glucoamylase (GluA). A mixture of monomers, solvents, and oil-soluble initiator was allowed to permeate through the micropores of SPG, suspended in an aqueous solution of poly(vinyl alcohol), and polymerized while retaining the narrow size distribution during polymerization. A small amount of acrylic acid or glycidyl methacrylate (GMA) was incorporated for the immobilization of GluA via covalent bonding. Although GluA has been regarded as being difficult to retain its activity after the immobilization process, a porous structure of the carriers definitely favored the immobilization, and a maximum 55% relative activity (RA) was obtained by the physical adsorption to PMMA spheres. The reaction of epoxide in GMA with 6-aminocaproic acid provided a spacer arm for the carboxyl group. An improvement of activity was expected by the incorporation of the spacer arms; however, barely noticeable activity was observed for PMMA carriers either by the physical adsorption or by the covalent bonding. A slight improvement was observed for PS carriers with spacers compared to the carriers without them. The diffusion process of oligosaccharides in the porous carriers seemed to retard the rate of hydrolysis in the case of largest carriers, 60 μm PS-DVB-AA spheres. The activity of immobilized GluA was retained during a long storage period of more than 150 days, some of them even increasing gradually, while the activity of native GluA dropped to zero after 100 days. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 2655–2664, 1997     

Homogeneous liquid–liquid extraction using perfluorooctanesulfonic acid and calcium and its application to the separation and recovery of vitamin B12

A new phase separation phenomenon was observed in which the perfluorooctanesulfonate ion (PFOS⁻) and calcium ion form an ion‐pair associator and the sedimented liquid phase occurs from the homogeneous aqueous solution. This phenomenon was observed in the neutral pH region at room temperature (25 °C). The optimum concentration conditions for the reagents were [PFOS⁻]_T = 7 × 10⁻³ mol dm^‐3 and [Ca²⁺]_T = 1.1 mol dm^‐3. When these findings were applied to the homogeneous liquid–liquid extraction of vitamin B₁₂, the extraction percentage (E) was 83% and the concentration ratio (ie V_a/V_s, where V_a is the volume of the aqueous phase and V_s is the volume of the sedimented liquid phase) was a maximum of 149. The recovery of vitamin B₁₂ was achieved by adding the propanol–acetone (20 : 80 v/v%) mixed solvent to the sedimented liquid phase; the vitamin B₁₂ precipitated and was filtered. Both the PFOS⁻ and Ca²⁺ were removed by dissolution in the mixed solvent. The recovery percentage of vitamin B₁₂ was 78%. © 1999 Society of Chemical Industry     

Computer simulation of turbine oil oxidation. 1: Consumption of a hindered phenol antioxidant in model hydrocarbon systems at 115°C

Computer simulation of the inhibited oxidation of model hydrocarbon systems representing turbine oils of different composition, hexadecane/tetralin mixtures containing di-tert-butyl pcresol (DBPC), has been achieved using the kinetic and mechanistic information obtained from fundamental hydrocarbon autoxidation and inhibition studies. The oxidation life, the time to complete consumption of DBPC and its reactive intermediates, was calculated using previously reported and newly measured absolute rate constants for reaction involved. The results of this calculation of oxidation life were in good agreement with values experimentally determined. The oxidation life has been found to decrease with increasing amount of tetralin in the mixtures. This can be explained by the increased rate of consumption of antioxidants, caused by an increase in the rate of free radical formation, via the direct reaction of hydrocarbons with oxygen, and via the homolytic decomposition of hydroperoxides. The observed decrease in oxidation life, however, is not significant, despite the fact that the addition of tetralin considerably increases the rate of free-radical formation. The relatively low sensitivity of oxidation life to the rate of free-radical formation caused by the addition of an easily oxidisable substrate can be attributed to the occurrence of a direct oxidation of antioxidants. That is, kinetic analysis for the consumption of antioxidants disclosed that antioxidant consumption mostly occurred not through the inhibition of oxidation, but through direct oxidation. The direct oxidation of antioxidants obeys the rate equation -d[AH]/dt = k₆[AH]^1.0[O₂]^1.5 where k₆ can be calculated, at various temperatures, from Arrhenius parameters obtained in this study (log (A/M⁻¹s⁻¹) = 9.6 and Ea = 22.6 kcall mol).     

Cholesterol synthesis and degradation in normal rats fed a cholesterol-free diet with excess cystine

Feeding a diet with excess cystine to rats resulted in hypercholesterolemia. To understand the mechanism of the hypercholesterolemia’ cholesterol synthesis and degradation’ bile acid content of bile’ and fecal steroids were determined. The in vivo incorporation of tritiated water into hepatic cholesterol’ and activity of hepatic 3-hydroxy-3-methylglutaryl-CoA reductase in rats fed a high-cystine diet were significantly higher than those in rats fed a control diet. The activity of hepatic cholesterol 7α-hydroxylase was similar between two groups. Little effect of cystine supplementation was found on fecal sterol excretion although there were some changes in biliary excretion of cholic acid derivatives. These results indicate that hypercholesterolemia caused by feeding of a high-cystine diet may be due to the stimulation of hepatic cholesterol synthesis.     

Crystallinity Analysis of Glass-Ceramics by the Rietveld Method

The crystallinity of multicomponent glass-ceramic mixtures has been analyzed via the Rietveld method, using powder X-ray diffractometry data. The Rietveld technique uses an internal standard but requires no calibration data to determine the total amorphous phase content of a mixture. This method of analyzing the crystallinity of synthetic mixtures gives high-precision results, with an error of generally less than ±3.0%, for several glass-ceramics.     

Change of Crystal Phases and Microstructure of Amorphous Si-C-N Powder by Hot Pressing

An amorphous Si-C-N powder with Y₂O₃ and Al₂O₃ powder as sintering additives was hot-pressed at 1900°C for 120 min in a nitrogen atmosphere. Changes in the crystalline phases and microstructure of the amorphous Si-C-N powder during sintering were investigated by X-ray diffractometry (XRD) and transmission electron microscopy (TEM). The defects at the fracture origins of the sintered bodies after bending tests also were investigated by scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). XRD showed that alpha-Si₃N₄ was formed initially from the amorphous Si-C-N by 1530°C, which then transformed to ß-Si₃N₄ at 1600°C. Also, a slight formation of crystalline SiC occurred during the transformation from alpha- to ß-Si₃N₄, and it increased after the transformation was completed at 1900°C. TEM revealed that many SiC nanoparticles were incorporated into ß-Si₃N₄ grains after the transformation from alpha- to ß-Si₃N₄ at 1600°C. They were located at the triple points of the grain boundaries of ß-Si₃N₄ after continued Si₃N₄ grain growth at 1900°C. Besides the SiC nanoparticles, large agglomerations of carbon or SiC particles of 20-60 µm size were observed by SEM and EPMA at the fracture origins of the sintered bodies after the bending tests.